1. Field of the Invention
The present invention relates to a pilot recovery and audio mode detection mechanism, and more particularly, to a pilot recovery and audio mode detection mechanism implemented by a statistics algorithm.
2. Description of the Prior Art
Currently existing audio standards, such as audio parts of analog modulated TV systems (e.g., NTSC, PAL, and SECAM) or FM radio, have evolved from a single-channel playing mode into a multi-channel playing mode supporting stereo and bilingual modes. In order to achieve such a goal, different ways are adopted in different audio standards (e.g., BTSC, EIAJ, A2, or FM radio). But the similarity between them is that a pilot signal is modulated by a predetermined control signal and then added into signals at a transmitter to tell a receiver which audio mode has been adopted. Correspondingly, the receiver must have a mechanism for receiving and synchronizing the pilot signal and simultaneously decoding the predetermined control signal to determine the adopted audio mode.
Traditionally, a mechanism for synchronizing the pilot signal and detecting the audio mode is implemented by an analog phase-locked loop (PLL) in conjunction with an AM decoder. But drawbacks of this approach are that reliability of its detecting result often varies with environment temperature and time. In some documents, detecting audio mode is implemented by an all-digital phase-locked loop (ADPLL) in conjunction with a band-pass filter and an energy detector, but this suffers from higher costs. Hence, how to overcome such drawbacks under low operations becomes an important topic of the field.